Conventional modeling has problems in describing multi-party interactions. There are two main problems:
The first problem is that it requires creating a large amount of messages in various patterns. There is a high risk of missing an interaction in such a multi-party interaction environment.
The second problem is that a highly complex software system typically contains multiple sub-systems at various levels that need to interact with external systems, and these software systems and their sub-systems typically are developed and maintained by different development teams. It is very difficult for these development teams to communicate effectively with each other about the complex interactions. In particular, it is hard to ensure the accuracy and completeness for software systems to handle these interactions.
For these two reasons, conventional ways for modeling and developing multiple interacting software systems are very difficult and inefficient.